Induced electron emission spectrometer having a unipotential sample chamber

ABSTRACT

An induced electron emission spectrometer is disclosed which includes a conductive sample enclosure operable at a potential independent of the potential applied to the spectrometer slit defining electrode of the spectrometer. The sample enclosure includes a wall portion made of a metallic foil to define an Xray window through which the sample is irradiated with X-rays to induce electron emission from the sample.

United States Patent l l l NH l l l Inventors John C. Helmet Menlo Park: Norbert H. Welchert, Pllo Alto, both ol, Calil. Appl No 825.680 Filed May 19, 1969 Patented July 27. I971 Assignee Vlricu Associates Palo Alto. Calif.

INDUCED ELECTRON EMISSION SPECTROMETER HAVING A UNIPOTENTIAL SAMPLE CHAMBER 7 Claims, 3 Drawing Figs.

US. Cl 7, 250/495, 250/4 l .9 Int. Cl H01] 37/26 Field ol Search 250/495, 4 I .9

[S6] Relerences Cited UNITED STATES PATENTS 3,374,346 3/ I968 Watanabe 250/49 5(1) 3,46l,306 8/1969 Stout ct alum 250/49.S(1)

Primary Examt'ner- Archie R. Borchelt Assistant Examiner-A. L. Birch Attorneys-Stanley Z Cole and Leon F. Herbert ABSTRACT: An induced electron emission spectrometer is disclosed which includes a conductive sample enclosure operable at a potential independent ofthe potential applied to the spectrometer slit defining electrode of the spectrometer. The sample enclosure includes a wall portion made ofa metallic foil to define an X'ray window through which the sample is irradiated with X-rays to induce electron emission from the sample.

P CMPUTER COUNTER PULSE AMPLIFIER PATENIED JUL27 I971 SHEET 1 GF 2 w J 1 SE25 W T $152 ,w J 3 1 n @238 @228 wfim J2EE: ma mas INVENTORS JOHN C HELMER NORBERT H. EICHERT BY ATTO Y INDUCED ELECTRON EMISSION SPECTROMETER HAVING A UNIPOTENTIAL SAMPLE CHAMBER DESCRIPTION OF THE PRIOR ART Heretofore, induced electron emission spectrometers have employed a probe insertable into the spectrometer through a gastight port in a wall thereof. The sample material was carried on the probe for irradiation with X-rays to induce electron emission from the sample. The energies of the electron emission were analyzed to produce an energy spectrum of the sample. However, when insulative sample materials were to be analyzed it was found that the electron emission from the insulative sample material produced a nonuniform potential over the emissive surface of the insulator and this caused the output energy spectrum to have extremely poor resolution. A spectrometer of this prior art type is disclosed and claimed in copending US. Pat. application No. 763,69I, filed Sept. 30, I968 and assigned to the same assignee as the present invention.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved induced electron emission spectrometer.

One feature of the present invention is the provision of a conductive enclosure surrounding the sample, such enclosure being operable at a potential independent of the potential at the spectrometer slit, and having an aperture in registration with the spectrometer slit for passage of induced charged particle emission from the sample enclosure into the analyzer of the spectrometer.

Another feature of the present invention is the same as the preceding feature wherein a portion of the sample enclosure is made of metallic foil to define an X-ray window through which the sample is irradiated with X-rays from a source externally disposed of the sample enclosure.

Another feature of the present invention is the same as any one or more of the preceding features wherein the sample enclosure includes a hollow cylindrical outer shell into which a sample probe is slidably inserted for introducing the sample into the sample enclosure.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic line diagram, partly in section and partly in block diagram form, depicting an induced electron emission spectrometer incorporating features of the present invention,

FIG. 2 is an enlarged sectional view ofa portion of the structure of FIG. I delineated by line 2-2 and FIG. 3 is a sectional view of the structure of FIG. 2 taken along line 3-3 in the direction of the arrows. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. I and 2, there is shown an induced electron emission spectrometer l incorporating features of the present invention. The spectrometer 1 includes a hollow cylindrical evacuated envelope 2. The envelope 2 is maintained at an operating pressure of approximately torr via an internal vacuum pump 10. A sample probe 3 is slidably inserted into the envelope 2 through a gastight vacuum lock at port 4. A thin cylindrically shaped sleeve of sample material 5 to be analyzed is carried on the probe 3 and is held by the probe 3 in a position to receive X-ray radiation from an annular source 6 of X-rays coaxially disposed of the probe 3 and sample 5.

A noninductive filamentary thermionic cathode emitter 7 is concentrically disposed surrounding the X-ray source 6. The source 6 is operated at a relatively high positive potential relative to that of the emitter 7 such that the source 6, as of aluminum is bombarded by a stream of electrons to produce the X-ray radiation. A focus electrode 8 focuses the electron stream onto the X-ray'source 6. A grid 9, which is operated. at ground potential, is disposed surrounding the sample 5 in LII between the sample 5 and the X-ray source 6 for preventing electrons generated in the region of the X-ray source 6 from traveling toward the region of the sample probe 3.

A generally cylindrically shaped conductive shell 11, as of aluminum or copper, coaxially surrounds the sample 5. The shell 11 includes a wall portion 12, which is disposed on an imaginary straight line between the X-ray source 6 and the sample 5, and which is made of metal foil to form an X-ray window. X-rays emanating from the X-ray source 6 pass through the window I2 to irradiate the sample 5. In a typical example. the foil I2 is of aluminum and is 0.0003inch thick, see FIG. 3. The foil 12 is wrapped into a self-supporting cylinder and is retained in position by being located inside four longitudinally directed metal struts I3, as of aluminum.

The shell II includes an annular slit-shaped aperture I4, as of 0.006-inch wide. disposed in registration with an immediately adjacent an annular spectrometer entrance slit l5 defined by the annular gap formed between the inner marginal lip I6 a ring-shaped plate electrode I7 and the adjacent end I8 of a hollow cylindrical metallic electrode I9. The slits I4 and 15 are spaced apart by a distance which is preferably equal to or less than the width of the slits such that the two slits appear as one slit to electrons emitted from the sample and entering the spectrometer through slits l4 and I5. In a typical example, the slits 14 and 15 are spaced apart by 0.040-inch.

The shell II is supported in position within the grounded electrode structure via a ring-shaped insulative plate 21 which in turn is carried within a central aperture 22 in plate electrode 17. A second cylindrical insulator 23, as of alumina, supports the shell II from a tubular grid support member 24.

The sample probe 3 includes a insulative core rod 25, as of alumina, with an outer conductive nonmagnetic cylindrical jacket 26, as of aluminum. The shell II and the jacket 26 are electrically connected together via nonmagnetic spring contacts 27, as of Elgaloy spring wire, carried from the jacket 26. The jacket 26 and shell II form a conductive generally to roidal-shaped enclosure or chamber 33 operating at a unipotential which is independently variable relative to the potential applied to electrodes I7 and I9, which define the spectrometer entrance slit IS. A sweep generator 31 supplies a potential to the enclosure 33 via jacket 26 which can be swept between 0 and +2,000 v. relative to the potential applied to the spectrometer entrance slit defining electrodes 17 and I9. In this manner, a swept electron retarding potential is established between the sample 5 and the spectrometer entrance slit 15 for energy selection of the emitted electron, as admitted into the energy analyzer portion of the spectrometer.

The unipotential chamber 33 is defined by the region bounded by shell II and jacket 26 and it permits insulative sample material 5 to be analyzed with high resolution of the energies of the emitted electrons because the electron current leaving the insulative surface is replaced by an equal and opposite electron current flowing from the inside walls of the chamber to the insulative sample material, such that an equipotential is maintained everywhere inside the chamber 33. The chamber 33 also permits high resolution analysis of the energies of electrons emitted from gaseous samples introduced into chamber 33. Such gaseous samples may con veniently be introduced into chamber 33 from a source of gas, not shown, via an axially directed gas passageway 34 (See FIG. 3) coaxially disposed of the ceramic core 25, such passageway 34 communicating with chamber 33 via radial bores 35 passing through core 25 and jacket 26.

The X-ray window I2 is preferably disposed in an out-ofsight path from spectrometer entrance slit 15 such that photoelectrons liberated by X-ray absorption in the window 12 do not pass through the slit I5 into the energy analyzer region.

The sample probe 3 is slidably inserted into shell II and the insulative core 25 is slidably received within a bore 37 in the cylindrical electrode I9 such that the sample probe 3 is posi' tioned in precise concentricity with the shell I I.

The analyzer region of the spectrometer is indicated at 38 in F 1G. I and includes a spherical condenser 39 with a positive voltage applied to the inner spherical member 41 and a negative potential applied to the outer spherical member 42. A pair of grounded conical metal shields 43 and 44 are disposed at opposite ends of the spherical condenser for shielding the electron stream from the fringing fields of the condenser 39. The conical plates include condenser entrance and exit slits 45 and 46, respectively, in registration with the central electron path through the spherical condenser 39. The spherical condenser focuses electrons passing through the spectrometer entrance slit 15, located at a first focal plane, to an annular spot at a spectrometer exit 47 located at a second focal plane. The exit slit 47 is defined by the gap between the inner periphery of a centrally apertured plate 48 in the second focal plane and the adjacent end of a cylindrical electrode 49. The exit slit defining electrodes 48 and 49 are operated at ground potential.

A plurality of focusing electrodes 51 are disposed at intervals around the outer periphery of the spherical condenser exit slit 46. lndependently variable potentials are applied to these electrodes 51 from a source of variable potential 52 for correcting circuitry of the electron image as focused at the spectrometer exist slit 47. A centrally apertured plate 53 is disposed at the electron image crossover plane. The diameter of the central opening 54 in the plate is chosen to collect those electrons outside of a certain predetermined aberration range.

After the electrons pass through the spectrometer exit slit 47 they pass into a cylindrical condenser 55 formed by inner cylindrical electrode 49 and outer cylindrical electrode 56, which is operated at a negative potential relative to the grounded inner electrode 49. The cylindrical condenser 55 causes the electrons to be focused at the entrance opening 57 of an electron multiplier 58. Each electron which enters the electron multiplier 58 produces an output pulse across load resistor 59. The output pulse is coupled via coupling capacitor 61 to a pulse amplifier 62 which amplifies the pulse and feeds it to a counter 63. The counter 63 counts the pulses and feeds the count to a time averaging computer 64, such as a CAT- 400. The internal sweep of the computer 64 is synchronized with the output of the sweep generator 31 which sweeps the retarding potential applied between the probe 3 and the spectrometer entrance slit 15. With each sweep, the computer 64 performs a multichannel addition and storage operation. which when read out on an oscilloscope or X-Y plotter produces a graphical representation of the energy spectrum of the sample scanned by the spectrometer.

The unipotential chamber 33 permits high resolution analysis of photoemitted electron energies when employing insulative or gaseous samples 57 It is also useful for analysis of conductive samples 5.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What I claim is:

I. In an induced electron emission spectrometer, means for irradiating a sample material so as to cause charged particles to be emitted therefrom, means forming an electrode having a spectrometer slit therein disposed proximate the sample material so that the emitted particles are caused to pass through said slit, charged particle detection means. energy analyzing means disposed between said spectrometer slit and said detection means for focusing charged particles of selected energies into said detector means, all the improvement comprising, means forming a conductive enclosure substantially enclosing the sample material, said enclosure having an opening for passage of the emitted charged particles therethrough to said spectrometer slit, and means for insulatively supporting said sample enclosure relative to said spectrometer slit defining electrode means, whereby said sample enclosure is operable at a potential independent of the potential of said spectrometer slit defining electrode means.

2. The apparatus of claim I wherein said opening in said sample enclosure is a second slit, said second slit being disposed immediately adjacent said spectrometer slit in substantial registration therewith.

3. The apparatus of claim 1 wherein said means for irradiating the sample material includes a source of X-rays, said sample enclosure including a portion made of a metal foil to form an X-ray window disposed between said X-ray source and the sample such that X-rays emanating from said X-ray source pass through said foil to the sample.

4. The apparatus of claim 1 wherein said sample enclosure is apertured and means forming a conductive probe insertable into said sample enclosure through the apertured portion of said enclosure. said probe serving to introduce the sample into said sample enclosure.

5. The apparatus of claim 4 wherein said probe is slidably insertable into said sample enclosure, and means forming spring contacts for producing electrical contact between said probe and said sample enclosure.

6. The apparatus of claim 5 wherein said sample enclosure is cylindrical, and said probe is axially insertable of said cylindrical sample enclosure.

7. The apparatus of claim 6 wherein said sample material is formed as a relatively thin sleeve of sample material coaxially disposed of and carried upon the exterior surface of said probe. 

1. In an induced electron emission spectrometer, means for irradiating a sample material so as to cause charged particles to be emitted therefrom, means forming an electrode having a spectrometer slit therein disposed proximate the sample material so that the emitted particles are caused to pass through said slit, charged particle detection means, energy analyzing means disposed between said spectrometer slit and said detection means for focusing charged particles of selected energies into said detector means, all the improvement comprising, means forming a conductive enclosure substantially enclosing the sample material, said enclosure having an opening for passage of the emitted charged particles therethrough to said spectrometer slit, and means for insulatively supporting said sample enclosure relative to said spectrometer slit defining electrode means, whereby said sample enclosure is operable at a potential independent of the potential of said spectrometer slit defining electrode means.
 2. The apparatus of claim 1 wherein said opening in said sample enclosure is a second slit, said second slit being disposed immediately adjacent said spectrometer slit in substantial registration therewith.
 3. The apparatus of claim 1 wherein said means for irradiating the sample material includes a source of X-rays, said sample enclosure including a portion made of a metal foil to form an X-ray window disposed between said X-ray source and the sample such that X-rays emanating from said X-ray source pass through said foil to the sample.
 4. The apparatus of claim 1 wherein said sample enclosure is apertured and means forming a conductive probe insertable into said sample enclosure through the apertured portion of said enclosure, said probe serving to introduce the sample into said sample enclosure.
 5. The apparatus of claim 4 wherein said probe is slidably insertable into said sample enclosure, and means forming spring contacts for producing electrical contact between said probe and said sample enclosure.
 6. The apparatus of claim 5 wherein said sample enclosure is cylindrical, and said probe is axially insertable of said cylindrical sample enclosure.
 7. The apparatus of claim 6 wherein said sample material is formed as a relatively thin sleeve of sample material coaxially disposed of and carried upon the exterior surface of said probe. 